EE152 Green Electronics
Batteries
11/5/13
Prof. William Dally
Computer Systems Laboratory
Stanford University
Course Logistics
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Tutorial on Lab 6 during Thursday lecture
Homework 5 due today
Homework 6 out today
Quiz 2 next Thursday 11/14
AC Input/Output Summary
•  AC is just slowly changing DC
–  But need to store energy during the “nulls”
•  Power factor = Preal/Papparent
–  Want power factor very close to 1
–  Requires current proportional to voltage
•  PF correcting input stage
–  Controls input current – sine x error
•  Grid connected inverter
–  Controls output current
•  Independent inverter
–  Control output voltage
–  Use a full-bridge to generate a PWM Sine Wave
•  Pulse width proportional to sin(x)
–  LC Filter to reject high frequencies
Anti-Islanding
•  Grid-connected inverters need to turn off when the grid
goes down.
•  Safety issue for firemen, linemen, etc…
•  How do you detect when the grid goes down?
Anti-Islanding
•  Line monitoring
–  Voltage limits, frequency limits.
–  Rate of change of frequency
–  Rapid phase shift
•  Active detection
–  Impedance measurement
–  Forced phase shift/frequency shift
Batteries
Batteries
•  Many Green Electronic systems require energy
storage
•  Batteries are widely used to store energy in chemical
bonds
•  Model as dependent voltage source
•  Care required in charging and discharging
Energy Density
Device
Energy Density
MJ/kg
Gasoline
44
Lithium Ion Battery
1.7
Lead Acid Battery
0.15
Two Dimensions of Energy Storage
Editorial
Figu
power
comb
F i g ure 3. Simplified Ragone plot of the energy storage
domains for the various electrochemical energy conversion
cells,
ment
Energy Density vs Battery Chemistry
Lithium Polymer
250
Prismatic
200
WattHours/Kilogram
Lithium Phosphate
150
100
Lithium Ion
Cylindrical
Aluminum Cans
Prismatic
Nickel Cadmium
Cylindrical
Prismatic
50
Lead Acid
Nickel Metal Hydride
Cylindrical
Prismatic
50
100
150
200
250
WattHours/Litre
300
350
400
450
Photo of Pack
18650 Cell
Tesla Pack
Battery Model
LB
RB
+
VBS
VB
-
VBS depends on state of charge and temperature
Panasonic 18650
Cell Type NCR18650B
Specifications
Rated Capacity (at 20 )
Nominal Capacity (at 25 )
3350mAh
Nominal Voltage
Charging Method
Charging Voltage
Charging Current
Charging Time
Ambient Temperature
Charge
Discharge
Storage
Weight (Max.)
64.93mm
Dimensions(Typ.) H
of
D
18.2mm
Bare Cell
d
7.9mm
Discharged State after Assembling
2G23X0KYKU
Dimensions (Max.)
Maximum size without tube
Volumetric Energy Density
Gravimetric Energy Density
Min.3200mAh
Min.3250mAh
3.6V
Constant Current
-Constant Voltage
4.2V
Std.1625mA
4.0hrs.
+10 +45
-20 +60
-20 +50
47.5g
(D)
18.25mm
(H)
65.10mm
676Wh/l
243Wh/kg
Discharge
Characteristics
NCR18650B1S
DischargeTemperature
Rate Characteristics
for for
NCR18650B
cell-1
4.5
Temp:25
1.-20 2.-10
3.0
4.25
5.40
6.45
Charge:CC-CV:1.625A-4.2V
(65.0mA cut) cut)
Charge:CC-CV:1.625A-4.20V(65.0mA
Discharge:CC:Variable
Current (E.V.:2.50V)
Discharge:CC:3.25A(E.V.:2.50V)
7.60
Cell Voltage / V
4.0
2G23X0KYKU
3.5
3.0
2.0CA
1.0CA
0.5CA
0.2CA
2.5
2.0
0
500
1000
1500
2000
2500
3000
Discharge Capacity / mAh
3500
4000
DischargeTemperature
Temperature Characteristics
forfor
NCR18650B1S
Discharge
Characteristics
NCR18650B
cell-1
1.-20
4.5
2.-10
3.0
4.25
5.40
6.45
Charge:CC-CV:1.625A-4.20V(65.0mA cut)
Discharge:CC:3.25A(E.V.:2.50V)
7.60
Cell Voltage
e / V
4.0
G23X0KYKU
3.5
3.0
40
25
0
-10
-20
2.5
2.0
0
500
1000
1500
2000
2500
3000
Discharge Capacity / mAh
3500
4000
Charge Characteristics
Charge
Characteristicsfor
forNCR18650B1S
NCR18650B
4.5
Charge:CC-CV:1.625A-4.20V(65.0mA cut)
No.1
5000
4000
3.5
3000
Capacity
3.0
2.5
2.0
2G23X0KYKU
2000
45
25
0
1000
Current
0
60
120
Charge Time / min
180
240
0
4000
Capacity / m
mAh
4.0
Current / m
mA
Cell Voltage
e / V
Cell Voltage
3000
2000
1000
Lead-Acid Charge Cycle
Battery Current
IB
IC
IT
Battery Voltage
VC
VF
VT
trickle
t0
bulk charge
tB
completion
tC
Time
float
tF
High Charge Voltage Reduces Life
Deep Discharge Reduces Life
High Temperature Reduces Life
Particularly at high SOC
Lead-Acid Charge Cycle
Battery Current
IB
IC
IT
Battery Voltage
VC
VF
VT
trickle
t0
bulk charge
tB
completion
tC
Time
float
tF
Layered Control
Vbat
State
Machine
State
Ibat
V or I
Control
Imax
IM1
PWM
Current
Control
G
Lead-Acid Charging States
VMax>V≥VC
Reset,
V<0,
V>VMax
VB>V≥VT
Off
Off
VT>V≥0
Trick
I = IT
V≥VT
Bulk
I = IB
V≥VC
Comp
V = VC
I<IF
Float
V = VF
Charging Power Path
CT
F1
D1
200:1
Vi
400V
Vac
G
Ci
1mF
M1
Vx
D2
GND
input stage
switched inductor
L1
Vo
50 H
Co
1mF
output
filter
RCS
.005
Vbat
Cells
One Cell
~2.0V for lead-acid
~3.2V for LiFePO4
~3.7V for LiCo
Capacity depends on volume
0.4Ah to 200Ah or more
1.28Wh to 640Wh
Series Connection Increases Voltage
Ah remains the same
100 LiFePO4 cells is about 320V (280-360)
Capacity (in Ah) the same as one cell
128Wh (0.4Ah cells) to 64kWh (200Ah cells)
Series Parallel vs Parallel Series
Which is preferred (assuming same Volts and Ah)?
Battery Management Tasks
•  Charge control
–  CC, CV profile
–  Cell balancing
–  Temperature monitoring/control
•  SOC (state of charge) estimation
–  Fuel gauge
–  Integrate power
–  Estimate from voltage, current, and temperature
•  Lifetime extension
–  Avoid deep discharge
–  Avoid high-charge, high-temperature storage
Cell Balancing
Maximum cell voltage must not
be exceeded during charging
Voltage of each cell must be
monitored
Current must be “bled off” of
high-voltage cells before they
exceed Vmax
Simple resistive balancer or
flyback to recycle energy
When Things go Wrong
Battery Summary
•  Batteries store energy in chemical bonds
•  Model as dependent voltage source with series R and L
•  Terminal voltage is a function of charge state Q
–  Also a function of temperature and charge rate
•  Area of charge-discharge curve is loss in battery
•  Cells connected in series and parallel to build large batteries
(series connection of parallel cells)
•  Cells must be balanced to avoid overcharge
•  Battery management
–  Charge control
–  Fuel gauge
–  Lifetime extension
Grounding
Ground
•  Exactly one point in your circuit is GND
–  An arbitrary point that we refer to as having 0 Volts potential
–  All other voltages are referenced to this point
•  Connections to GND should be made in a Spider not a
Daisy Chain
Good
Bad
Ground Loops
•  Avoid loops
Why Ground Loops are Bad
Consider The PV Lab Power Path
A Poor Way to Ground This
Why?
Grounding Resistor Introduces a Loop
Grounding Summary
•  Single-point ground
•  Avoid loops
Debugging
Debugging
•
Get one thing working at a time
–  Work from input of circuit to output
–  Work with simple stimulus, then more complex
•
Form a hypothesis and test it
–  Don’t just randomly change things
–  Work from the schematic
–  Calculate voltage on each node and then verify it.
•
If a chip isn’t doing what it should
–  Check every pin of the chip
–  Vdd, GND, all inputs, all outputs
•
For current monitor
–
–
–
–
–
–
•
Check voltage across sense resistor
Check “bias” voltage for op-amp (0.45V)
Check that op-amp inputs have the expected voltage
Verify output voltage
Check with DC input first, then with operating MPPT
Check AC common-mode input voltage
Use a scope
–  Signals that look good at DC (on a multimeter) may have big AC problems
–  Signals that look good on a logic analyzer (digitized) may have big analog problems
Future Lectures
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Tutorial for Lab 6
Quiz 2 Review
Guest Lectures Tesla, Renovo, Enphase
Wrapup
Project Presentations